This invention relates generally to the atomization of fluids, and is particularly useful for the atomization of highly viscous fluids such as fluids containing particulates.
Atomization plays an important role in many industrial processes from oil or waste combustion to ceramic powder synthesis. Most atomizers are one of three main types, pressure atomizers, two-fluid atomizers, and rotary cup atomizers. Pressure atomizers are relatively simple and inexpensive, but are easily plugged by solids and cannot handle high viscosity liquids. Two-fluid atomizers are slightly less prone to plugging, but still have difficulty handling viscous fluids and tend to be expensive to operate because of the need for high-pressure atomizing gas or steam. Rotary cup atomizers can be effective, but have the major disadvantage of being more mechanically complex.
Even for those applications for which conventional atomizers are used, the droplet size distribution can have a significant impact on the economics and efficiency of the process. There is a lower bound on the mean particle size that can be produced, and the maximum particle size can be several orders of magnitude larger than the mean particle size. Therefore, even if the mean particle size is within the specified size range for processes such as metal atomization, the larger sized particles may be outside the desired size range thus significantly lowering the process yield. Further, since heat transfer and combustion reactions are much more efficient for small particles, the large particles in the distribution result in most of the unburned hydrocarbons in combustion and incineration operations.
One problem is obtaining very small droplet size in viscous fluids. It is generally not attainable with rotary cup atomizers. Pressure atomizers are limited to droplets of about twice the size of the orifice, so physical size, pressure drop and surface tension problems make this type generally unsuitable. Two-fluid atomizers can produce tiny droplets, but only with very high pressure atomizing gas and very high gas flow ratios (mass ratio of atomizing gas to mass of liquid atomized). Ultrasonic atomizers can achieve tiny droplets, but are inherently much more complex and expensive.
Another problem is plugging of the atomizer by solid particles in the fluid. Pressure atomizers, due to the small orifice, have serious plugging problems. Many two-fluid atomizers achieve high performance at the cost of small passages and associated plugging problems.
Accordingly it is an object of this invention to provide an improved method for atomizing a fluid.
It is another object of this invention to provide a method for atomizing a fluid which can be used to effectively atomize a highly viscous fluid.
It is another object of this invention to provide an improved method for atomizing a fluid so as to generate very small droplet sizes.
It is another object of this invention to provide an improved method for atomizing a particle laden fluid without plugging.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention which is:
A method for atomizing a fluid comprising:
(A) heating a gas to a temperature of at least 300xc2x0 F. to produce a hot gas;
(B) passing the hot gas through an opening to produce an accelerated hot gas stream;
(C) contacting the accelerated hot gas stream with a flow of atomizable fluid; and
(D) applying shear, pressure and inertial forces from the accelerated hot gas stream to the flow of atomizable fluid and atomizing the atomizable fluid.
As used herein, the term xe2x80x9catomizingxe2x80x9d means to make in the form of many droplets.
As used herein, the term xe2x80x9cshear forcexe2x80x9d means the tangential force applied to the surface of a fluid by another fluid when the two fluids are travelling at different velocities.
As used herein, the term xe2x80x9cinertial forcexe2x80x9d means a force exhibited by a body or fluid when it is accelerated or decelerated by other external forces.
As used herein, the term xe2x80x9cpressure forcexe2x80x9d means the normal force acting at a point in a fluid or at a surface as a result of molecular motions.